Hydrogenation of an oil increases the saturated fatty acid content of the oil, while decreasing the unsaturated fatty acid content. During the hydrogenation process, trans fatty acids also are formed. The extent of saturation and trans formation depends on the hydrogenation reaction conditions, including type of catalyst, reaction temperature, and reaction time. Hydrogenation is used to increase shelf-life of oil products and to increase functionality. In general, harder products such as stick margarine have a higher trans fatty acids content than softer products such as soft tub margarine. As saturated and trans fatty acids intake have been linked to increased serum cholesterol levels in humans, it is generally recommended that intake of saturated and trans fatty acids be limited.